Nuisance: Whether diminution in value caused by Japanese knotweed was recoverable as a claim in nuisance (Davies v Bridgend County Borough Council – 2023)

Where the value of a property continues to be adversely impacted by Japanese knotweed, even after the property has been treated, is the diminution in value recoverable as a claim in nuisance rather than purely economic loss?

The background

In Davies v Bridgend County Borough Council [2023], the claimant acquired a property affected by Japanese knotweed which spread from neighbouring land owned by the defendant. The claimant bought the property in 2004, the knotweed was discovered in 2017 and the defendant was notified of the infestation in 2019.

The claimant brought a claim against the defendant in nuisance, and at first instance the court found that the defendant had knowledge of the infestation from around 2012-2013. The defendant was therefore found to be in breach of duty to prevent the nuisance from 2013 until treatment started in 2018.

The court at first instance found that the claimant had been unable to effectively treat the knotweed on his own land, because the defendant had continued to fail to treat the infestation on its property. Any attempt by the claimant to treat would have failed, because the infestation would simply return. The defendant had therefore breached its duty.

The claimant succeeded at first instance in its claim for liability but his heads of loss, including a claim for diminution in value of his property, were dismissed as economic loss rather than interference with enjoyment of the claimant’s land. The court referenced the decision in Network Rail Infrastructure Ltd v Williams, a leading authority on knotweed interference, which stated that nuisance did not protect economic interests. The claimant appealed.

The decision

The Court of Appeal found that the claimant was entitled to damages under a claim in nuisance for diminution in value.

Williams had not determined that the claimant could not be entitled to damages for economic losses, but stated that a loss of amenity must be caused by encroachment of knotweed in order to establish a nuisance. If the nuisance caused by encroachment of knotweed can be evidenced, and there is a diminution in value of the claimant’s property as a result, a claim for damages is valid.

In this case, knotweed had been treated and the encroachment was therefore historic. Nevertheless, the claimant claimed for a continued diminution in value of his property, even after treatment had taken place. The Court of Appeal found that the defendant’s continued failure to treat its property after it had become aware of the knotweed and its breach had prolonged the nuisance – and therefore the diminution in value – such that the ‘but for’ test in causation was met.

Advice and action for landlords

Landlords, developers and property managers are advised to be aware of this decision, and the potential for successful damages claims for diminution in value arising as a result of knotweed even after the infestation has been treated.

Prompt treatment of knotweed after becoming aware of an infestation, and appropriate steps to prevent continuation of a nuisance, should help to mitigate losses. In this decision, the defendant had failed to take prompt action to prevent the nuisance, which caused the claimant’s loss of amenity and economic losses to continue.